U.S. application Ser. No. 795,238, filed May 9, 1977 and now U.S. Pat. No. 4,173,720 describes the manner in which, when forming a tomogram, a rotating body is irradiated by a flat X-ray beam so as to achieve a large number of linear X-ray shadowgraphs, the so-called profiles, from which the tomogram is constructed by back projection. For eliminating the effects of the filter function, in accordance with one of the methods described therein the profiles should be convoluted with a suitable filter function prior to the back projection. For this purpose, the profiles are successively reproduced on the anode of an image intensifier tube and the resultant image is moved by means of suitably energized deflection coils mounted around the image intensifier tube. The image of the profiles as moving over the anode is detected by a photomultiplier tube through a mask in which the filter function has photographically been laid down.
A drawback inherent in this known method is that it is rather difficult to realize a well-defined and reproducible transmission characteristic representing the filter function in the mask by means of photographic techniques.